Field of the Invention
The present invention relates in a general manner to low-voltage DC power supply for electronic communication devices able to be used in a medium-voltage part of a power line carrier communication system.
Description of Related Art
A non-limiting field of application of the invention relates to remote reading systems for energy meters, particularly electricity meters. Certain electricity providers, such as the French company ERDF, are today in the process of deploying systems using the power lines of the power distribution network to allow communication, preferably two-way, of data between the electricity meters installed in the homes of users and hubs in charge of collecting the data from a set of meters. FIG. 1 schematically shows the configuration of such a system, indicating in the upper part of the figure the communication layer of the system facing the physical layer of an energy distribution network: an electricity meter 1 situated in the home 2 of a user exchanges data with a hub 3 using the low-voltage (typically between 220 and 400 volts) power lines 4 of the power distribution network. This so-called PLC (Power Line Carrier) technology consists in overlaying on the low-frequency electrical signal of the power distribution network (typically 50 Hz in France, or 60 Hz in the United States) a low-energy signal at a higher frequency, typically in the frequency band called CENELEC A (from 10 KHz to 95 KHz). When the hub 3 receives the data from various meters 1, it decodes them using a suitable PLC modem, and processes them with a view to retransmitting them to a central server 5 of the energy distributor by any appropriate WAN wide area communications network 5a. 
Apart from the hub, additional appliances can be added at the level of the medium-voltage part of the power distribution network. In particular, as the PLC signal weakens with distance, it may be necessary to regenerate it when the hub is too remote. To do this, as shown in FIG. 2, it may be necessary to add one or even several repeaters 6 to regenerate the PLC signal as many times as necessary all the way to the hub 3.
Whatever the appliance under consideration (hub 3, repeater 6 or any other electronic appliance able to inject and/or read the PLC signal), said appliance must be able to interface with the medium-voltage power line 8 by means of a coupling device. Today, this is achieved using a power line carrier coupler 9 electrically linked to the medium-voltage line 8 of the power distribution network. This coupler 9 must allow the passage of the PLC signal while rejecting the frequency of the electrical network, and must protect the appliance from the voltage of the electrical network and the transient voltages that could result from switching operations. FIG. 3 schematically illustrates a possible known embodiment for the coupler 9, in association with a hub 3. The coupler 9 essentially includes a coupling capacitor 10 and an isolation transformer 11 arranged in such a way that:                the coupling capacitor 10 is electrically linked on the one hand to the medium-voltage line 8 and, on the other hand, in series with the isolation transformer 11;        the secondary of the isolation transformer 11 is connected to the hub 3.        
A compensating module 10′ is interposed in series between the coupling capacitor 10 and the primary of the isolation transformer 11 to allow the filtering to be adapted, and in particular to obtain a low attenuation in the bandwidth of the PLC signal.
All the aforementioned electronic appliances include active components (microprocessors, amplifiers etc.) that must be powered by one or more DC voltage values, typically in the order of 3.3 volts or of 12 volts. Today, the hub 3 is generally situated at the level of a Medium-Voltage/Low-Voltage power transforming substation 7 of the power distribution network, which makes it possible to derive the voltage needed for the power supply from the low-voltage lines of the electrical network.
It is not, on the other hand, possible to envision placing the hub at another location, typically further upstream in the medium-voltage part of the network, unless a solution is found for supplying power to the active components. The repeaters themselves are placed on the medium-voltage part of the power distribution network, at locations where the low-voltage network is generally not present.